1. Field of the Invention
The present invention relates to a capacitor run motor. More specifically, the present invention relates to an improvement in a bracket arrangement for mounting bearings for a rotor in a capacitor run type single phase induction motor. 2. Description of the Prior Art;
Single phase induction motors have been widely used nowadays as a prime mover for driving a variety of relatively small sized machines. Various schemes for running single phase induction motors have also been proposed and put in practical use. A typical scheme for running a small sized single phase induction motor comprises generation of a rotating magnetic field by means of a main winding and an auxiliary winding wound in slots formed on the inner surface of an aperture of the stator core and a capacitor connected in series with the auxiliary winding for the purpose of advancing the phase of the current in the auxiliary winding with respect to that of the main winding. Such a motor is often referred to as a capacitor run motor. A more detailed structure of such a prior art capacitor run motor is considered in the following.
FIG. 1 is an end schematic view of the stator as wound of the windings of a typical prior art capacitor run motor. FIG. 2 is a side view of such a typical prior art capacitor run motor. Referring to FIG. 1, a stator core 7 comprises a stack of a plurality of core material plates of the shape as seen in FIG. 1. The stator core 7 as shown comprises a circle aperture and eight slots equally spaced apart from each other and extending in parallel with the axial direction of the stator core 7, whereby eight teeth are formed between the slots. A main winding 1 and an auxiliary winding 2 are wound in the slots around the periphery of two adjacent teeth of the stator core in the so called full pitch winding manner such that the main and auxiliary windings are dislocated by one tooth. As a result, in the motor shown, four main winding coils and four auxiliary winding coils are formed which extend through the slots in the axial direction of the stator core and turn at the opposite ends of the stator core in terms of the axial direction, while the coil ends at the opposite stator core ends each form a continuous mass 5 of coils in a ring shape protruding from the end surfaces of the core in the axial direction with the diameter slightly larger than that of the circle aperture of the stator core. A bracket 4 of half shell structure is mounted to the stator core 7 by fitting, through compression, the yoke 8 of the stator core 7 to the opening portion 6 of each half shell such that the stator core 7 is housed in the bracket 4 and bearings 3 provided in the bracket 4 support the shaft of a rotor. In view of the fact that the prior art motor of the type now in discussion comprises the coil ends at the opposite ends of the stator core 7 which are each of a continuous mass of coils in a ring shape, it is necessary that the inner geometry of the bracket is larger than the outer geometry of the coil ends of the stator. More specifically, the inner diameter of the bracket must be larger than the outer diameter of the above described coil end ring mass in the radial direction and the inner end walls of the bracket must be spaced from the end surface of the stator core sufficiently enough to clear the coil ends. Thus, the bracket of a motor of this type becomes somewhat bulky. Nevertheless, a motor of this type is often used as a prime mover in various small sized machines. Therefore, the bulk of the bracket of a motor of this type makes the machine bulky accordingly. Thus, it is most desirable that a capacitor run motor improved of the bulkiness of the bracket for the stator is provided without degrading the performance thereof. Another problem encountered in the illustrated prior art motor is that since the opening 6 of the half shell of the bracket is fitted to the periphery of the yoke 8 of the stator core high precision is required for the geometry of the opening 6 and the yoke 8, which makes complicated the cutting of the material for the bracket and the stator core and makes the cost expensive.
As to be discussed infra, the present invention employs a stator arrangement wherein image poles are used. Such a single phase induction motor as employs image poles has also been proposed. An example of a single phase induction motor employing a stator arrangement wherein image poles are employed is disclosed in U.S. Pat. No. 3,295,034, entitled "Two-Speed Single-Phase Electric Motor", issued Dec. 27, 1966 to George E. Herzog and assigned to Westinghouse Electric Corporation. More specifically, an image pole type induction motor is structured such that the stator comprises a half number of main and auxiliary poles of the same polarity to be excited by windings and the main and auxiliary windings are provided on the excited poles so as to form main and auxiliary image poles by way of opposite polarity of the half number of main and auxiliary excited poles, whereby the rotating magnetic flux is generated between main and auxiliary pairs of the excited and image poles. Presumably, such an image pole type induction motor must be advantageous in that a less number of main and auxiliary winding coils are mounted and hence the structure becomes simple and the assembly is fascilitated. Nevertheless, induction motors of such an image pole type have been very seldom put into market. The reason is presumably that although the number of winding coils is decreased by half, the number of turns of each of the winding coils must be increased accordingly and hence labor is required for that purpose, with the result that substantial labor is not saved, while another problem is encountered that some loss of magnetic flux is caused and efficiency of the power is accordingly decreased say by several percent. In the past, only for these reasons, designers of single phase induction motors, particularly capacitor run motors of a relatively small size have never thought of employment of an image pole stator arrangement.
A single phase induction motor comprising a main winding and an asymmetrical auxiliary winding has also been proposed. An example of such an induction motor having an asymmetrical auxiliary winding is disclosed in U.S. Pat. No. 3,433,988, entitled "Slab Side Motor With An Asymmetrical Starting Winding" and issued Mar. 18, 1969 to Harold B. Arnold and assigned to Emerson Electric Company. As known to those skilled in the art, a single phase induction motor with an asymmetrical auxiliary winding brings about an increased starting torque and an increased slip in terms of the maximum rotation speed as compared with a similar motor with a symmetrical auxiliary winding. Because of these characteristics, a single phase induction motor with an asymmetrical auxiliary winding can be advantageously used depending on applications. As become apparent from the following description, the present invention can be applied to a capacitor run motor with an asymmetrical auxiliary winding with particular advantage.